Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The present invention may find applicability in all such applications, although the description that follows will generally focus on the use of the invention within a spinal cord stimulation system, such as that disclosed in U.S. Pat. No. 6,516,227 (“the '227 patent”), issued Feb. 4, 2003 in the name of inventors Paul Meadows et al., which is incorporated herein by reference in its entirety.
Spinal cord stimulation is a well-accepted clinical method for reducing pain in certain populations of patients. A Spinal Cord Stimulation (SCS) system typically includes an Implantable Pulse Generator (IPG) or Radio-Frequency (RF) transmitter and receiver, electrodes, at least one electrode lead, and, optionally, at least one electrode lead extension. The electrodes, which reside on a distal end of the electrode lead, are typically implanted along the dura of the spinal cord, and the IPG or RF transmitter generates electrical pulses that are delivered through the electrodes to the nerve fibers within the spinal column. Individual electrodes are arranged in a desired pattern and spacing to create an electrode array. Individual wires within one or more electrode leads connect with each electrode in the array. The electrode lead(s) exit the spinal column and generally attach to one or more electrode lead extensions. The electrode lead extensions, in turn, are typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG or RF receiver is implanted. Alternatively, the electrode lead may directly connect with the EPG or RF receiver. For examples of other SCS systems and other stimulation system, see U.S. Pat. Nos. 3,646,940 and 3,822,708, which are hereby incorporated by reference in their entireties. Of course, implantable pulse generators are active devices requiring energy for operation, such as is provided by an implanted battery or an external power source.
There are several types of leads presently used in spinal cord stimulation. One type is a percutaneous lead, which can have electrodes linearly positioned on the distal portion of the lead. A conventional lead implantation procedure commonly places the linearly positioned electrode array parallel to the spinal cord column at or near the physiological mid-line. Precise placement of the electrodes relative to the target nerves is critical for achieving a satisfactory physiological response to electrical stimulation and for keeping stimulation thresholds low in order to conserve battery power.
In addition to precise placement of the electrode array, proper selection of the electrodes, i.e., which of the electrodes in the array should be active in a given patient, is critical for achieving effective stimulation therapy. However, because of the uncertainties of the distances of the electrodes from the neural target, the unknown nature of the specific conductive environment in which the electrode is placed, etc., it generally cannot be known in advance and with precision which combination of active electrodes will be perceived by a patient as providing optimal therapy. As a result, patient therapy generally requires at the outset that various electrode combinations be tried and feedback received from the patient as to which of the combinations feels most effective from a quantitative and qualitative standpoint. When one considers that the electrodes can be operated in many different modes (e.g., monopolar, bipolar, multipolar) and that a given electrode can operate as a current source or sink with variable relative current amplitudes, pulse durations, and pulse frequencies, it turns out that there can be many electrode combinations that might need to be tried on a given patient.
Therefore, it can be a difficult and time-consuming task to try every single electrode combination on a given patient, and trying all such combinations might not be possible in a given clinical setting, which at best may last for a few hours. As a result, because only a relatively small number of combinations can be tested, the results can be haphazard and can provide imperfect results because the best active electrode combinations to deal with the patient's chronic pain may be missed.
Accordingly, what is needed is a method of intelligently selecting the possible active electrode combinations to improve the accuracy and speed of this process.